Hitherto, there have been proposed various hydrogenated block copolymers of A-(B-A)n type or (A-B)n type (wherein n is an integer of 1 or more) which are composed of a polymer block (A) constituted mainly from an aromatic vinyl compound unit and a polymer block (B) constituted mainly from a conjugated diene unit and in which a carbon-to-carbon double bond derived from the conjugated diene unit is hydrogenated. The hydrogenated block copolymers have been used as an alternate material of vulcanized rubbers or soft vinyl chloride-based resins for production of various molded articles.
Also, it is known that polyolefin-based resins which are excellent in oil resistance, heat resistance, chemical resistance and processability but insufficient in flexibility, transparency and impact resistance are compounded with the above hydrogenated block copolymers to prepare polyolefin compositions which are improved in flexibility, transparency and impact resistance and free from generation of toxic gases when incinerated upon disposal thereof. The polyolefin compositions have been extensively used as an alternate material of soft vinyl chloride-based resins in various applications such as food transportation, parts of household appliances and medical devices (refer to Patent Documents 1 and 2).
However, tubes obtained by molding the polyolefin compositions prepared by compounding the polyolefin-based resins with the above hydrogenated block copolymers tend to frequently suffer from occurrence of undesirable phenomena such as collapse or break of the tubes because they fail to exhibit a sufficient resistance to deformation caused when bending the tubes into a ring shape or an arcuate shape. To solve such a problem, Patent Documents 3 and 4 disclose the methods for improving an endotracheal tube and a tube, respectively. However, the method described in Patent Document 3 has failed to sufficiently improve deformation, collapse, etc., of the tube, whereas the method described in Patent Document 4 tends to cause stickiness between the tubes owing to the use of a softening agent for rubbers therein, which results in poor handling property of the tubes. In particular, in medical applications, there tends to occur the problem that when clamping the tube with forceps, inner surface portions of the tube are stuck together, resulting in poor restoration of the tube into its original shape even after removing the forceps therefrom, or the problem that the tubes are stuck with each other after subjected to sterilization in an autoclave.
To solve the problem of stickiness between the tubes, Patent Document 5 discloses a soft polymer composition including a block copolymer composed of polystyrene and an ethylene-propylene copolymer, a block copolymer composed of polystyrene and an ethylene-butylene copolymer, and a polyolefin. However, the polymer composition still has the problem that its transparency is insufficient owing to poor compatibility between the block copolymers.
In addition, when used in medical applications, it is required that the tubes are coupled to various connectors. However, since the polyolefin-based resins are not dissolved in a solvent, the polymer composition containing a large amount of the polyolefin-based resins tends to show a poor adhesion strength upon bonding with a solvent. Patent Document 6 discloses a multi-layered tube comprising (a) a polypropylene-based resin and (b) a resin composition containing a polymer block constituted from an aromatic vinyl compound unit for the purpose of improving a solvent-bonding property thereof. However, owing to the multi-layered structure of the tube, it is difficult to form the respective layers having a uniform thickness.
Further, Patent Document 7 discloses a medical device such as tubes which comprises (a) a hydrogenated block copolymer obtained by hydrogenating a block copolymer composed of a polymer block constituted mainly from an aromatic vinyl compound unit and a polymer block constituted mainly from a conjugated diene compound unit, and (b) a high-crystalline propylene-based resin.
In the applications such as medical devices and food transportation, the tubes are frequently used under a low-temperature condition for maintaining a good quality of contents therein and, therefore, required to have an excellent performance capable of withstanding an impact force upon falling or dropping even under a low-temperature condition by which the tubes can be prevented from suffering from breakage, etc.    Patent Document 1: JP 2-300250A    Patent Document 2: JP 10-67894A    Patent Document 3: JP 2002-248671A    Patent Document 4: JP 2003-287163A    Patent Document 5: JP 4-159344A    Patent Document 6: JP 2001-1432A    Patent Document 7: JP 2004-194803A